Observation of nonparabolic conduction subbands in InGaAs/InAlAs multi-quantum wells by very-high-field pulse cyclotron resonance

Observation of nonparabolic conduction band is rather difficult because electrons normally occupy near the bottom of conduction band. Use of two-dimensional electron gas and Landau quantization made it possible to scan equivalent electron energy by a magnetic field. We report a clear evidence of a non-parabolic conduction subband in 5–10 nm wide InGaAs quantum wells in InGaAs/InAlAs multi-quantum well structures. Infrared optical transitions due to cyclotron resonance take place under pulsed high magnetic fields up to 100 T. In experiments, electron absorption is discriminated by a circular polarized light of a carbon dioxide laser. Water and methanol vapor lasers were also used to measure the mass of low-energy electrons. Measurements were made near 30 K.